Welcome to the G3ZPS Web Pages

Main Menu Navigation

Home Page

Antenna Pages

The extended double zepp or EDZ is one of the most successful wire antennas ever developed. It has a bit of gain and if high enough can be agreat antenna on the HF bands. I am not a great fan of compromise, especially if you have limited space or height. Traps and multiband antennas all have loss, matching problems or narrow bandwidth and will waste those precious watts of RF.

The 'Zepp' name came from the use of the antenna on Zeppelins in the 20's and 30's. Its a non resonant antenna which provides arounnd 3dB of gain over a dipole if mounted at the right height. Around 0.6 of a wavelength is ideal .

Each leg of the Zepp is 0.64 Wavelength (5/8) and must be fairly accurately cut, the formula I use is 599/f in MHz. There are a number of options for feeding the antenna, the first is to use 300 / 450 ohm feeder and run into a balanced ATU or transmatch. The second is to use the open wider feeder as a matching stub and add a 1/1 balun at the bottom. This link Zepps gives details of the length of the 450 ohm stub and the tap points. I have made Zepps for all the HF bands and change them as required

For really low loss make your own 450 ohm ladder line, there are a number of methods. A favourite is to use discarded ball point pens (the old biro type) as the spacers. The loss will be lower than commercial plastic line and its a bit of fun. The spacing is not critical, 2 - 3 inches will be in the right ball park.

Dipole Antennas

A huge amount has been written about the humble dipole antenna over the years, as a wire antenna it is perhaps unsurpassed in terms of simplicity and performance. You can bend it, turn into a V, shorten it and it still provides acceptable performance on its design frequency. All HF dipoles are easy and cheap to construct especially if you avoid any complex (and heavy) traps or balanced ATU's. I am a fan of monoband wire antennas, as they are so easy to make and can be changed. More complex multiband antennas are great (and you can buy them if you wish), but 100metres of wire and a few dipole centre pieces are really cheap to buy and you learn something when you make the antenna for yourself.

I currently have a monoband dipole for 80m (no traps) at about 10m above the ground and found it out performs long wires for my purposes. 10m above the ground is low on 80m and equate to .125wavelength. This has a profound affect on the radiation pattern of the antenna and produces a lot of high angle radiation. This is actually great for distances out to 700 - 1000miles after dark and reports are consistently very good. Considering that the amount of energy radiated at low elevations is quite small, its quite surprising that I can work into east coast US so easily and even into VK on rare occasions. In fact there a lot of myths that low antennas can't work DX, with a bit of clever operating they certainly can.. the trick is making the best of any limitations. If you are interested in working DX on 80m with limited power and antennas, check out this link AE5X

Resonating such an antenna can be hard as its difficult to measure the feed impedance at the antenna (unless you have a tower climb or have accurate half wave lengths of coax lying about) so there are compromises. At resonance and at this height its difficult to judge the actual resistive component of the antenna, it could in fact be below 50ohms. I used the shortest possible stub of UR43 coax and assessed where the SWR was lowest, then I trimmed accordingly (starting at 66ft per leg) to get the lowest SWR in the middle of the band, even then its possible that adding the feeder back to the shack will affect the SWR as the whole system does not have a constant impedance. Still, close to resonance and with reasonable match, feed losses should be quite low and antenna efficiency acceptable. Off course on 40m and 20m the electrical height is greater and the low angle performace is more useable...but then on 20 and up I make the Zepps, and they work even better!!!

This is a particularly good site for information on the performance of dipole antennas at differing heights, AA3RL Dipole pages

Material Copyright © 2002 {Steve Shorey}